Listing 2 contains the associated abstract base class that implements this new interface.

package step.three; import java.util.ArrayList; import org.apache.struts.util.LabelValueBean; /** * This absract class implements the required methods for an "Option * List" source, which returns the name/value pairs for the options * related to an HTML "select" tag. * * This class must be extended by a concrete subclass which must * implement the specified abstract method loadOptions() * to load the list of available options from the implementation-specific * data source. */ public abstract class OptionListSourceBase implements OptionListSource { private ArrayList options = null; private ArrayList optionsPlusBlank = null; /** * Returns a filtered array of LabelValueBean * objects defining the available options. * * This method will return the same results as using the method * getOptions(filter, true). * * @param filter an implementation-defined filter parameter * further identifying or limiting the available options * @return an ArrayList of LabelValueBean * objects defining the available options */ public ArrayList getOptions(Object filter) { return getOptions(filter, true); } /** * Returns a filtered array of LabelValueBean * objects defining the available options. * * The default implementation of this method ignores the * filter and invokes the unfiltered getOptions() * method. Implementations that require filtered options should * override this method with the appropriate implementation- * specific code. * * @param filter an implementation-defined filter parameter * further identifying or limiting the available options * @param required a boolean indicating whether or not input is * required for this field. Setting this indicator to false will * cause the generation of an additional option for no selection. * @return an ArrayList of LabelValueBean * objects defining the available options */ public ArrayList getOptions(Object filter, boolean required) { return getOptions(required); } /** * Returns an ArrayList of LabelValueBean * objects defining the available options. * * This method will return the same results as using the method * getOptions(true). * * @return an ArrayList of LabelValueBean * objects defining the available options */ public ArrayList getOptions() { return getOptions(true); } /** * Returns an ArrayList of LabelValueBean * objects defining the available options. * * @param required a boolean indicating whether or not input is * required for this field. Setting this indicator to false will * cause the generation of an additional option for no selection. * @return an ArrayList of LabelValueBean * objects defining the available options */ public ArrayList getOptions(boolean required) { if (options == null) { loadOptionsArrays(); } if (required) { return options; } else { return optionsPlusBlank; } } /** * Obtains the available options from the implementation-specific * load method. */ protected void loadOptionsArrays() { loadOptions(); if (options == null) { options = new ArrayList(); System.out.println(this.getClass().getName() + ".loadOptions() produced no result."); } optionsPlusBlank = new ArrayList(); LabelValueBean blankOption = new LabelValueBean("-- No Selection --", ""); optionsPlusBlank.add(blankOption); optionsPlusBlank.add(options); } /** * Loads the list of available options from the implementation-specific * data source. */ protected abstract void loadOptions(); /** * Sets the ArrayList of LabelValueBean * objects defining the available options. * * @param options the ArrayList of LabelValueBean * objects defining the available options */ protected void setOptions(ArrayList options) { this.options = options; } }